Supporting characters are a lot more interesting when there's something weird about them. While you don't want to give every single GMC the characters meet a quirky trait (unless you're playing a David Lynch-style game), important or recurring characters will be more memorable if they've got an unusual trait. The list below is for modern games, but most of them will work for other settings if you tweak the details a bit.

Believes that he is the descendant of Emperor Norton I, and expects to be treated accordingly

Is constantly trying to solve a Rubik's Cube

Is obsessed with Tom Brokaw

Always wears a Star Fleet uniform

Claims that he invented Google and was screwed out of his share of the company

Always trying to give people creepy neck messages

Has an incredibly annoying, high-pitched voice

Break dances whenever possible

Always wearing the perfect hat for the occasion

Full-blown paranoid conspiracy nut

Talks like John Wayne

Carries a pocket full of peanuts that he eats constantly and just throws the shells on the floor no matter where he is

Dresses like WHAM!

Won't shut up about the time he met Tom Arnold

Constantly getting into arguments with his ventriloquist's dummy

Gives everyone nicknames

Only speaks in song lyrics

Drives an AMC Pacer Wagon painted in swirling day-glow colors

Carries a Lincoln Hawk action figure in his pocket, which he consults when making decisions

Won't stop quoting Monty Python and the Holy Grail, no matter how much you beg